Compression of Space for Low Visibility Probes

Abstract

Stimuli briefly flashed just before a saccade are perceived closer to the saccade target, a phenomenon known as perisaccadic compression of space (Ross et al., 1997). More recently, we have demonstrated that brief probes are attracted towards a visual reference when followed by a mask, even in the absence of saccades (Zimmermann et al., 2014a). Here, we ask whether spatial compression depends on the transient disruptions of the visual input stream caused by either a mask or a saccade. Both of these degrade the probe visibility but we show that low probe visibility alone causes compression in the absence of any disruption. In a first experiment, we varied the regions of the screen covered by a transient mask, including areas where no stimulus was presented and a condition without masking. In all conditions, we adjusted probe contrast to make the probe equally hard to detect. Compression effects were found in all conditions. To obtain compression without a mask, the probe had to be presented at much lower contrasts than with masking. Comparing mislocalizations at different probe detection rates across masking, saccades and low contrast conditions without mask or saccade, Experiment 2 confirmed this observation and showed a strong influence of probe contrast on compression. Finally, in Experiment 3, we found that compression decreased as probe duration increased both for masks and saccades although here we did find some evidence that factors other than simply visibility as we measured it contribute to compression. Our experiments suggest that compression reflects how the visual system localizes weak targets in the context of highly visible stimuli.

Repeatedly Flashed Luminance Noise Can Make Objects Look Further Apart

“…These examples stress the power of other visual objects to bias the perceived location of masked stimuli. Previously, we have found strong attraction of a masked probe towards a stable reference (Born et al., 2016; Zimmermann et al., 2014); that is, the opposite of the current bias. However, the probe was only briefly flashed (<50 ms).…”

“…In the first experiment (Experiment 1a), observers judged the distance between alternating bars, comparing a condition with a luminance noise pattern presented during the off-phase of the stimuli to a condition without luminance noise. Based on our previous findings (Born et al., 2016; Zimmermann et al., 2014), my initial hypothesis was that masking of apparent motion results in underestimations of the spacing between bars in the condition with noise. Surprisingly, however, observers judged the spacing between bars as wider with noise (Figure 2(a)).…”

“…But can luminance noise also affect where we perceive an object or change the perceived distance between objects? Recently, we have found strong attraction of a briefly presented probe towards a stable reference when the probe was presented close in time to a flashed full-screen luminance noise pattern (Born, Krüger, Zimmermann, & Cavanagh, 2016; Zimmermann, Born, Fink, & Cavanagh, 2014). Further, a small jump of a peripheral target bar is harder to see when accompanied by flashed luminance noise (Zimmermann et al., 2014; Zimmermann, Morrone, & Burr, 2013).…”

Fixation related shifts of perceptual localization counter to saccade direction

“…Mislocalization of flashed stimuli can also occur during fixation. Some studies have reported that a briefly flashed stimulus followed by a mask is mislocalized toward a visual anchor in a pattern similar to saccadic compression (Zimmermann, Born, et al, 2014;Born, Krüger, Zimmermann, & Cavanagh, 2016). To test whether we could reproduce this effect, and whether it would also produce mislocalization toward the fixation point, we measured localization after backwards masking, closely following the experimental protocol of Zimmermann, Born, et al (2014).…”